The premature detonation of munitions, including artillery rounds, bombs, missiles, and/or mortar shells during handling, shipping, or in storage creates a highly dangerous condition. Various safety and arming (S&A) devices have been proposed in the prior art for preventing accidental arming and premature detonation of munitions. A safety and arming device is now a required element of a munition to ensure that the munition is not armed and detonated prior to the intended time therefore. The safety and arming device is part of a munition's fuze and prevents arming of the fuze until certain conditions are met. Many safety and arming devices require two conditions or occurrences for operation and initiation of the fuze. The first condition utilized is typically setback acceleration, which is associated with the launching of the munition. Setback acceleration of the munition is a convenient condition to sense and measure. The second condition can be based on a number of different parameters, such as barrel escape velocity, timing, sensing and/or counting the turns or rotations of the munition, etc.
One early safety and arming device is the percussion fuze. A percussion fuze is normally held inoperative by a safety device which is released by setback forces developed upon launching a projectile. Such a fuze is shown in U.S. Pat. No. 1,652,635, to Pantoflicek, issued Dec. 13, 1927.
Another proposed safety and arming device includes a fuze wherein movement of a setback slider mechanism pivots a lever. The movement of the lever activates a timing mechanism. The timing mechanism releases a detonator carrier which is moved into an armed position. One such device is shown in U.S. Pat. No. 2,863,393, to Sheeley, issued Dec. 9, 1958.
Still another type of fuze device was proposed in which a slide mechanism responds to setback forces developed during sustained acceleration of a projectile to arm the fuze. Typical devices of this type are disclosed in U.S. Pat. Nos. 2,595,757, to Brandt, issued May 6, 1952; 4,284,862, to Overman et al, issued Aug. 18, 1981; and 4,815,381, to Bullard, issued Mar. 28, 1989.
Other examples of prior art devices that use the setback acceleration condition to arm a fuze include zig-zag gravity weights; escapement mechanisms, such as gravity weight drive escapements; successive falling leaves; and various combinations of such devices. More modem fuzes integrate such features in smaller packages, by employing micro-electromechancial systems (MEMS) based technology and processes, based upon lithographic techniques, or offshoot techniques such as plating, molding, plastic injection, and/or ceramic casting—examples of such applications of MEMS technology are disclosed in a series of patents to Robinson and Robinson et al., including U.S. Pat. Nos. 6,167,809, issued Jan. 2, 2001; 6,568,329, issued May 27, 2003; 6,964,231, issued Nov. 15, 2005; and, 7,316,186, issued Jan. 8, 2008. Such more modern fuzes comply with MIL-STD-1316 or STANAG 4187 standards, requiring that two unique and independent aspects of the launch environment must be detected either mechanically or electronically by the fuze, before the weapon can be enabled to arm itself; including set-back acceleration, rifling-induced spin, gun- or launch-tube exit, airflow, and flight apex. Further, such modern fuzes typically perform targeting functions, which can include electromagnetic or electrostatic target detection, range estimation, target impact detection, grazing impact detection, or timed delay. The best methods to accomplish these functions and provide the required S&A device depends on the characteristics of the weapon system, such as limitations on size, onboard power, desired configuration, and factors such as affordable cost, material selection and compatibility, and safety and reliability standards.
U.S. Pat. No. 6,964,231, incorporated herein by reference, discloses a MEMS fuze (hereinafter the '231 fuze) for medium caliber munitions, such as a 20-mm bursting projectile, designed to meet criteria such as being relatively inexpensive (on the order of several dollars when manufactured in large quantities); extremely small to allow maximum room for the most lethal payload practicable; extremely reliable, to perform under battlefield conditions; and preferably requiring no pre-launch power, since the battery typically does not activate until launch. The '231 fuze incorporates 3 major interlocks in its S&A device: (1) an initial motion of a setback slider in response to acceleration; whereby, the setback slider removes a setback lock lever tab from an arming slider's setback lock catch (a rather complex action), thereby freeing the arming slider; (2) which arming slider under urging of the spin imparted to the projectile, moves part way to arming; whereupon it is impeded by a catch tab, against a command lock catch face within the arming slider; (3) electronics within the fuze, i.e. the fuze circuit, initiates a pre-programmed signal, a signal which may be timed, based upon rotation count, or other desired criteria, to fire a piston against a rocker piston tab, which moves a lock rocker assembly in a complex three dimensional manner, to move the catch tab so as to free the arming slider to continue its motion into the armed position. Once in the armed position, a continuous fire initiation path is established and once the electronics initiate firing, the projectile will explode. Such a continuous, MEMS fire initiation path is disclosed within U.S. Pat. Nos. 7,055,437, and 7,069,861, both to Robinson, et al., issued Jun. 6, 2006 and Jul. 4, 2006, respectively, and both of which are hereby incorporated herein by reference.
As shown in FIG. 15 of U.S. Pat. No. 6,964,231, there is an inflection point, the pivot bend, located at the middle of the three dimensional lock rocker assembly, which is a stress point that has sometimes failed in prototype samples. A prototype '231 fuze has a footprint of approximately 10×10 mm, a relatively large footprint; a rather complex means whereby an independent setback slider initially frees an arming slider; a certainly complex three dimensional lock rocker assembly which finally releases the arming slider to proceed to its armed position, all of which are certainly significant advantages versus conventional (non-MEMS-based) fuzes of the prior art; but there still exist problems in size, reliability, complexity, and cost, regarding the optimum possible fuze, to meet the stated criteria.